1. Field of the Invention
This invention relates to an apparatus and method for producing individual portions of predetermined size from larger blocks of deep-frozen foodstuffs. More particularly, the invention relates to such an apparatus and method wherein the frozen block is a block of frozen fish and wherein two series of cuts are necessary to form the portions of predetermined size.
2. Description of the Prior Art
It is common practice aboard commercial fishing boats or trawlers to process fish and form frozen blocks from the processed fish. For blocks frozen at sea certain measurements have for reasons of processing technique proven to be optimal and have today practically become international norms, namely approximately 800-810.times.505-510.times.60-65 mm., e.g., 806.times.508.times.62.5 mm. The most critical of these dimensions is the height. The thinner the block is made, the more labor-consuming and thus expensive is its production. In view of the especially high wage costs aboard ships, any reduction in block thickness therefore signifies a noticeable increase in production costs. On the other hand, an increase in block thickness causes a retardation in the flow of heat in freezing, which leads to an impermissible decrease in quality when a thickness of approximately 60 to 65 mm. is exceeded, principally due to the formation of crystalline ice needles which bore through the cell walls and can lead to the loss of cellular fluids when the fish is thawed. The length and width measurements of the block have proved through practical experiences to be a serviceable compromise between manageableness on the one hand and optimal weight on the other.
Numerous factors influence the size of the fish sticks to be finished from the block--namely the following: At least one dimension (thickness) should be small enough to guarantee a rapid flow of heat during cooking and yet large enough so that, together with another dimension (width), it gives the form enough stability so that it can be comfortably handled, while the third dimension (length) should be so adjusted to the other two that the volume of the rectangular solid corresponds to a handy morsel. The dimensions which have been found through trial and error to be optimal on the basis of these requirements, namely (11-12).times.(19-20).times.(80-85) mm., e.g., 11.5.times.19.times.83 mm., corresponding to a weight of 28.5 g., or 11.5.times.20.times.83 mm., corresponding to a weight of 30 g., have become unofficial standards for the Common Market.
A number of procedures have been developed for the production of individual portions from larger blocks of deep-frozen foodstuffs, e.g., for the production of fish sticks from frozen blocks of fish fillets. One obtains qualitatively excellent products (i.e., fully identical to the original material in structure, texture, and taste) by means of the division of the deep-frozen blocks into discs of strips through the use of thin saws or grinding wheels at temperatures ranging between -15.degree. C. and -30.degree. C. Also, in some cases, further double cutting of these discs or strips is required in directions transverse to the first cutting direction to obtain the final product.
One of the disadvantages of the previously described technique is that a substantial portion of the original material (generally 8 to 15%) is waste, either as fish "sawdust" or as slime. Even if this waste portion can be made usable in some form or other and does not represent a total loss, it is saleable or re-usable only at a much lower price than that of the original material or that of the finished product.
Thus, there have been numerous attempts to avoid or limit these losses during separation.
One such attempt or process involves the thawing of the block before its division and, when necessary, the refreezing of the individual portions. There is such a great loss in quality that today this process is hardly used.
Another known process for the practically loss-free division of a block of deep-frozen foodstuffs, in particular the division of a frozen block of fish filets into individual portions, is described in German Pat. No. 2,045,059. According to this reference, a block is placed in a pressing chamber at a temperature between -10.degree. C. and -30.degree. C. A plunger under pressure then presses the block out of the chamber through an immoveable wall having a number of openings. The openings are narrowed in the direction of egress and form pressure-proof channels enclosed on all sides. The block flows in a series of strips through the openings. During this procedure, pressure is maintained at least until pressure on the plunger, which has fallen below an initial value during the extrusion, has again built up to at least the initial value. During the pressing process, one is careful not to allow the temperature in the mass of the foodstuff to exceed a critical level determined by the fat content of the original material to be processed, normally between -10.degree. and -15.degree. C. Preferred working pressures are above 180, in particular above 240 at. The majority of the openings narrowed in the direction of egress are formed by a blade lattice arranged checkerboard-style and enclosed by a pressure-proof wall.
The structure, texture, and taste of the original material are frequently maintained very well when the initial block is divided according to this process. It is possible to directly obtain lengths of such width and thickness as is customary, e.g., for fish sticks, that need only be cut to a desired length. Sometimes, a loss of quality arises in the application of this process, primarily because the finished product exhibits a taste which is too "dry". Systematic investigations have shown that this undesired effect always arises if a pressing ratio is applied which is too high, primarily when the ratio is greater than 1.6:1. The term pressing ratio is used to identify the change in diameter of the material as it passes through the narrowed openings. The change occurs as a result of the extension of the material in the direction of the flow and is proportional to the amount of extension.
With the apparatus described in German Pat. No. 2,045,059, a pressing ratio less than 2.5:1 is often difficult to maintain, particularly with the processing of material which requires a pressure higher than approximately 150 at. In order to be able to withstand the great stress created by the high pressure, the blades forming the openings must be constructed with a minimal thickness of between 7.5 and 8 mm. This creates a problem in the production of lengths with the cross section customary for fish sticks (approximately 11 to 12 mm. by 18 to 20 mm.). Use of a lattice formed of blades of this thickness results in a pressing ratio of about 2.5:1, which is within a tolerable range of a 3:1 (maximum) but which is nevertheless still significantly above the range recognized through research to be optimal, i.e., a maximum of 1.6:1.
Subsequent suggested processes, see German Offenlegungsschrift No. 2,142,341.6 and German Offenlegungsschrift No. 2,222,205.5, utilize devices that keep the pressing ratio within certain limits, namely a maximum of 3:1 and preferably below 2:1. These devices utilize narrowed openings, through which the material is pressed at the same high pressure and low temperatures as in the previously discussed process, which are constructed as a single (or a unit constructed of at most two parts) tapered, pressure-proof forming channel instead of as a blade lattice.
In this way any desired pressing ratio, even one below the minimal values required for this process (viz., 1.1:1) can in fact be maintained. Nevertheless a simultaneous division of the block into a number of lengths, as in the first-cited process, is impossible.